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Haemoglobin. Molecular model of haemoglobin, a metalloprotein that transports oxygen around the body in red blood cells. It has four iron-containing haem groups (spheres). The rest of the haemoglobin structure consists of four globin proteins (amino acid chains, coils). Each globin protein is wrapped around a haem group, protecting it from being oxidised and destroyed by the oxygen it is intended to transport. The iron within each haem group reversibly bonds to oxygen and carbon dioxide in the blood.